Lancets are used in analytical-diagnostic applications to withdraw a small amount of blood from a part of the body (usually the finger or the earlobe) by pricking the lancet into the body part to generate a wound. If done manually, specially, trained personnel are required for this purpose. However, puncturing is associated with considerable pain.
Blood withdrawal systems consisting of a puncturing device and corresponding lancets which are specifically adapted to the corresponding puncturing device have been in use for a long time. Typically, a housing of the puncturing device contains a lancet drive by which a lancet is punctured mechanically through the skin. The driving element for the puncturing motion is a spring. Early in the development very simple designs were common in which the lancet was attached directly to one end of a compression spring which was arranged in an elongated housing. An example of such a lancing devise is shown in U.S. Pat. No. 4,469,110.
However, blood withdrawal systems of this type fail to satisfy the difficult requirements that must be met when the regular monitoring of certain analytic blood values are required. This particularly applies to diabetics who have to monitor their blood sugar level frequently in order to keep this level within certain limiting values by suitably adapting the insulin injections. Scientific investigations have shown that an intensive therapy involving at least four blood analyses per day can dramatically reduce the extremely severe late consequences of diabetes mellitus such as retinopathy which eventually leads to blinding of the patient.
However, with such intensive therapy it is desirable that the withdrawal of blood is associated with as little pain as possible. Numerous blood withdrawal systems aiming for an improvement in this area have been developed.
A typical withdrawal of blood by means of a blood withdrawal system requires two basic functions. Firstly, the puncturing device must be brought to a state in which it is ready for puncturing by tensioning the drive spring. This is called the “cocking phase”. Subsequently, the lancet drive is triggered and the relaxing motion of the drive spring drives the lancet. This is called the “drive phase”.
In previous blood withdrawal systems, the puncturing phase was the kinematic reverse of the cocking phase. In other words, the drive was cocked simply by pushing the lancet, after puncturing, back into its original position in which the spring was tensioned.
However, better results, in particular with regard to the lowest possible pain level while keeping the handling simple, are achieved when the lancet drive is designed such that the two functions are uncoupled from each other. Accordingly, it is preferable that in a cocking phase, the motion of an actuation element of a cocking mechanism is transmitted by an input-side coupling mechanism to the drive spring such that the spring is tensioned. And in a drive phase, the relaxing motion of the drive spring is transmitted by an output-side coupling mechanism to the lancet such that the lancet performs the puncturing motion at high speed.
The two coupling mechanisms usually consist of different structural elements. In any case, the motions performed during the two phases differ from each other (rather than being the kinematic reverse of the other phase). Blood withdrawal systems of this type are known, for example, from the following publications: U.S. Pat. No. 4,442,836; U.S. Pat. No. 5,318,584; U.S. Pat. No. 6,409,740; U.S. Pat. No. 6,419,661; and EP 1 254 632 A1.
Despite the extensive development efforts which resulted in the constructions described in these documents and numerous others, there is a strong interest to have a blood withdrawal system which optimally satisfies the difficult and to some extent contrary requirements i.e minimal pain sensation, simple handling, compact design as slim as possible, cost-efficient fabrication. Therefore, there is a need in the industry to improve the design of such blood withdrawal systems that will satisfy such requirements.